Orthodontic brackets attached to teeth engage an archwire that exerts forces upon them to move the teeth. Such brackets typically include an archwire slot for reception of the archwire. An archwire slot can have any desired cross-sectional configuration or size to match the size and shape requirements of the archwire, or archwires, that are to be engaged within the slot.
Orthodontic brackets today are typically bonded to a tooth with the archwire slot oriented parallel to the occlusal plane. However, the slot can also be angularly oriented across the bracket when desired.
Most brackets in use today include cleat extensions referred to as tie wings or lugs. they project upwardly and downwardly in pairs at the top and bottom of the installed bracket, respectively. These extensions conventionally permit the archwire to be held within the archwire slot of the bracket by means of a twisted wire (ligature) or an elastomer O-ring.
Numerous attempts have been made to design brackets that are self-ligating. A detailed discussion of patents and publications describing various closures that have been proposed for the archwire slots of such orthodontic brackets can be found in U.S. Pat. No. 5,094,614 to Wildman, issued Mar. 10, 1992, which is hereby incorporated into this disclosure by reference.
The Wildman patent discloses a slidable closure that engages the front of the archwire. The closure is recessed from the front or anterior surfaces of the disclosed bracket. This is also true of sliding closures shown in U.S. Pat. No. 2,549,528 to Russell, which was issued on Apr. 17, 1951, U.S. Pat. No. 2,671,964 to Russell et al., which was issued on Mar. 16, 1954 and in U.S. Pat. No. 3,131,474, which was issued on May 5, 1964 to Johnson. The fact that such recessed sliding closures require the archwire also to be recessed within the archwire slot before the closure can be moved over the archwire makes it very difficult for the user to visually confirm that the archwire is properly seated within the archwire slot to facilitate closing of the slidable cover.
When using a conventional bracket and tying wires, proper seating of the archwire can be confirmed by visually noting that the anterior surface of the archwire is flush with the anterior surface of the bracket. It is desirable that a self-locking bracket provide similar visual reference capabilities to the user. This cannot be attained where no anterior surface of the bracket is available for visually referencing the position of an archwire within the archwire slot of the bracket.
A self-ligating bracket designed to mount an archwire flush with an anterior surface of an orthodontic bracket to facilitate visual positioning of the archwire during orthodontic treatment is shown in my earlier U.S. Pat. Nos. 5,275,557 (Jan. 4, 1994), 5,429,500 (Jul. 4, 1995) and 5,466,151 (Nov. 14, 1995). These patents are hereby incorporated into this disclosure by reference.
The bracket embodiments disclosed within my previous patent disclosures utilize a ligating slide or closure that is permanently retained on the bracket during use, whether the closure is left in an open or closed condition. This guards against accidental release of the closure while the bracket is worn on a tooth.
Most importantly, the closure was designed to leave the usual tying extensions that protrude from the top and bottom of the bracket fully accessible to other orthodontic attachments for the application of torsional forces to the teeth. The exposed tying lugs remain always available for repositioning of the bracket and tooth by use of tying wires or other conventional attachment systems. One achievement of this bracket is the provision of a ligating slide within a bracket that maintains the normal features of protruding tie wings or lugs required by the profession.
The bracket embodiments of my earlier patents also include a closure in the form of a ligating slide that can complete a continuous tube surrounding the archwire when the closure is in a closed position. This can be effectively achieved in a Siamese or twin bracket configuration without covering or interfering with projecting extensions on the bracket.
Another recent patent pertaining to a self-ligating orthodontic bracket is U.S. Pat. No. 5,322,435, issued to Pletcher on Jun. 21, 1994. The patent discloses a locking slide member that is flat and guided by upright slots formed along both sides of the bracket and spanning the archwire slot. A resilient member or detent is provided to retain the slide member in either the open or closed position. No tie wings or lugs are included in the illustrated bracket forms.
Miniaturization of orthodontic brackets is extremely important today in view of the development of modern high-technology archwires. Patients desire small brackets to reduce the visual impact of the brackets while they are being worn. Orthodontists desire smaller brackets in order to more effectively use the biasing forces available in the high technology archwires, it being recognized that the force applied to a bracket by the archwire is decreased with increasing bracket spacing between teeth.
One drawback to miniaturization of the brackets shown in my earlier patents is the fact that most of the embodiments wrap the cover over the sides of the bracket to engage grooves posterior to the archwire slot across the bracket. The thickness of the sliding cover therefore increases the total width of the bracket beyond that which is necessary due to the strength properties of the bracket itself. It is subject to tooth contact due to normal occlusion clearances in the mouth
While the Pletcher U.S. patent does show a flat cover sliding within the lateral confines of a bracket, the guiding arrangement for the cover includes slots at both the superior and inferior sides of the archwire slot, thereby obscuring visual access to the critical corners of the archwire slots at the side edges of the bracket. Without this visual access being clear, one installing an archwire within a bracket cannot be certain as to proper seating of an archwire within the archwire slot before the slide cover is moved to a closed position.